Carbon Worlds -- Carbon-rich Planets

[Widdekind]

Some Exoplanets could be Carbon-rich, instead of Oxygen-rich. Such would be composed of Carbon-Silicon compounds ("Carborundum"), instead of Oxygen-Silicon compounds ("Silicates"). They could have mountains made of Diamond, and oceans of Tar.

Extrasolar Carbon planets, Space Art, Astronomy, Extrasolar planets

Their carbonaceous nature would make them different from silicate planets. The atmospheres might be smoggy, filled with carbon mono- or dioxide and other gases. If the temperatures are low enough (below 350 K), it is possible that gases could photochemically synthesize into long-chain hydrocarbons, which can rain down to the surface. These hydrocarbons range from compounds like methane (which can easily freeze, if the temperature is cold enough) to gasoline, crude oil, tar, or asphalt. The surface might be covered with tar-like precipitation. There might be a great lack of water on a carbon planet. The equivalences of the geological features present on Earth, such as mountains and rivers will likely be present on a carbon planet too, though with different compositions. The rivers could consist of oils for example and the mountains of diamonds and silicon carbides.

As long as water is somehow supplied to these planets (from cometary impacts for example), carbon planets should be able to support life.
Below the crust where the pressure is high enough, it is very likely that a thick layer of diamonds exists. It is possible that during volcanic eruptions diamonds from the interior would come up to the surface, creating mountains of diamonds and silicon carbides.

At the center carbon planets may have an iron core, or possibly a core of steel since the carbon may have reacted with the iron. The layer above the core will contain carbides (silicon and titanium carbides) that might be molten.

SPACE.com -- Diamond Planets: Rich Possibilities for Other Worlds

The planets in our solar system formed from a disk of gas and dust left behind from the Sun's formation. In regions where there was extra carbon or a lack of oxygen, carbon compounds like graphite and carbides would condense out of the mix, instead of stone...



Another set of candidates for diamond-laden planets are the Dark Worlds orbiting a dead, fast-spinning star known as PSR 1257+12. These planets -- three of them are roughly Earth-sized -- might have been formed by the destruction of a carbon-rich star, Kuchner said...


Carbon planets might also be common near the center of the galaxy, where stars are known to contain more carbon than out here on the spiral arms where our solar system resides, some 26,000 light-years from the galactic middle...


Carbon planets might have smoggy atmospheres laden with carbon dioxide, and a surface covered with tar-like precipitation. "A little bit like Los Angeles," Kuchner said.

Carbon-rich planets may boast diamond interiors - space - 08 February 2005 - New Scientist

Bizarre planets with internal layers of diamond many kilometres thick may form in carbon-rich areas of the galaxy, a new study suggests.


The diamond-rich planets could form from the dusty protoplanetary discs found around many stars, if they are rich in carbon and poor in oxygen, says Marc Kuchner at Princeton University, New Jersey, US.


Composed largely of heat-resistant carbides and graphite - as well as diamond - these planets could withstand much higher temperatures than terrestrial planets or gas giants, he says. This might account for giant non-gas planets found surprisingly close to other stars.


Although terrestrial life is based on carbon, the Earth is made largely of silicates. It contains only about 44 parts per million of carbon. However, the element is 1000 times more common in chondrite meteorites, which originated in the Solar System, though probably in a different region of the protoplanetary disc. Curious about these compositional differences, Kuchner and Sara Seager of the Carnegie Institution of Washington, US, studied prospects for building planets from the carbon-rich material of the meteorites.


The key factor behind the difference between carbon and silicate-based planets is the chemistry of the protoplanetary disc. Changing the ratio of carbon to oxygen "makes a huge difference to what condenses out", says Kuchner.


High oxygen levels produce silicate-based planets like the Earth, Venus, and Mars. But high carbon levels cause carbon compounds to condense out of the disc and clump together, producing carbon-based planets.

Like the Earth, a carbon-based planet would have a metallic iron core, but the surrounding layers would be different, they suggest. Above the core would be a thick layer of silicon and titanium carbides, extremely hard ceramics known for their impressive heat-resistance. Graphite would form above the carbide, with high pressure converting the bottom of the graphite layer to a shell of crystalline diamond.


A carbon-based planet would be oxygen poor, with a tarry hydrocarbon surface and an atmosphere rich in hydrocarbons and carbon monoxide. Future planet-hunting telescopes might be able to spot one by looking for carbon monoxide's distinctive spectral signature.


As long as water could somehow be delivered to their surfaces after they formed, such planets should be able to support life forms, Kuchner told New Scientist.


"Life on a carbon planet would be strange," he says. Oxygen-containing materials would be flammable in its hydrocarbon atmosphere, so metabolism might be the inverse of terrestrial life - burning oxygen as food rather than carbon compounds.


Older stars tend to spew more carbon, so as the Universe ages, carbon planets may become more likely, he says. They may already be more common near the ancient galactic nucleus, says Kuchner.

[Widdekind]

According to the article The Star that Ate a Mars in the 18 July 2009 AD issue of Science News (pp. 22-25):

[In 2006 AD], astronomers reported ultra-violet evidence that a carbon-rich disk orbits the star Beta Pictoris, 60 light-years away [from Earth], and could spawn Carbon Planets.

[Dani2010]

I dont think life can evolve on a such planet...